SymbolicHamiltonian.terms setter invalidates the object

[BrunoLiegiBastonLiegi]

SymbolicHamiltonian provides a setter for terms that do not take care of updating the form.
This means that by doing the following for instance:

from qibo.symbols import Z, X
from qibo.hamiltonians import SymbolicHamiltonian

h0 = SymbolicHamiltonian(Z(0)*Z(1) + Z(2)*Z(1), nqubits = 3)
h1 = SymbolicHamiltonian(X(0)*X(1) + X(2)*X(1), nqubits = 3)
print(h0.form)
h0.terms = h1.terms
print(h0.form)

you make its form and terms inconsistent.
I would say, in general, that terms should not have a setter since it is computed starting from the form and I would rather make it a @cached_property probably. At the moment the main reason why it is there, I believe, is beacuse it makes it easier to compose hamiltonians through the __add__ operator for instance, without the need to recompute the terms.